Current-driven periodic domain walls injection in a ferromagnetic nanostrip with a modified perpendicular magnetic anisotropy region

Effective control of domain wall (DW) injection and motion in a ferromagnetic nanostrip is of great significance for the development of DW-based spintronic devices. In this work, we exploit the properties of 90 degrees magnetization walls induced by a modified perpendicular magnetic anisotropy (PMA) between the out-of-plane and in-plane magnetized regions of Pt/Co, with spin-transfer torque (STT) being used to control the injection of DWs into a ferromagnetic nanostrip. We demonstrate that this STT stimulus combined with the modified PMA enables the continuous and synchronous injection of a series of head-to-head and tail-to-tail transverse in-plane DWs. Furthermore, micromagnetic simulation results show that the presence of a 90 degrees magnetized transition region is a prerequisite for magnetic DW injection, and that the generation frequency can be controlled reversibly from the MHz to the multi-GHz range. Our findings demonstrate the feasibility of a highly tunable and direct-current-controlled transverse in-plane DW signal source, which could pave the way toward compact and integrated DW circuits and oscillators.